Working with Files

BASIC Commands
LOAD	Retrieve a file from a device.
SAVE	Store a file to a device.
VERIFY	Verify that a file is written properly.
OPEN	Open a communications channel.
CLOSE	Close a communications channel.
CMD	Redirect standard output to a channel.
GET#	Get a byte of data from a channel.
INPUT#	Get bytes from a channel.
PRINT#	Write bytes to a channel.

KERNAL Routines
SETNAM	Set name of a file or channel.
SETLFS	Device selection and options.
LOAD	Retrieve or verify a file from a device.
SAVE	Store a file to a device.
OPEN	Open a channel.
CLOSE	Close a channel.
CLALL	Close all channels.
CHKIN	Set a channel to input mode.
CHKOUT	Set a channel to output mode.
CHRIN	Get a byte from a channel.
CHROUT	Write a byte to a channel.
READST	Read I/O status.

File Types
SEQ Sequential data
PRG Program file

Preparation		SETLFS, SETNAM
Send	.A	0 for LOAD, 1 for VERIFY
	.X	Low byte of loading address (if opened w/relocation)
	.Y	High byte of loading address (if opened w/relocation)
Stack usage		0
Address		$FFD5, 65493
Returns	.A	undefined
	.X	Low byte of ending address
	.Y	High byte of ending address

Preparation		SETLFS, SETNAM
Send	.A	Zero-page location of Starting Address pointer
	.X	Low byte of Ending Address
	.Y	High byte of Ending Address
Stack usage		0
Address		$FFD8, 65496
Returns	.A	undefined
	.X	undefined
	.Y	undefined

Preparation		SETLFS, SETNAM
Send	.A	ignored
	.X	ignored
	.Y	ignored
Stack usage		0
Address		$FFC0, 65472
Returns	.A	undefined
	.X	undefined
	.Y	undefined

Preparation		none
Send	.A	Length of filename
	.X	Low byte of address of filename
	.Y	High byte of address of filename
Stack usage		2
Address		$FFBD, 65469
Returns	.A	preserved
	.X	preserved
	.Y	preserved

Preparation		none
Send	.A	File number
	.X	Device unit number
	.Y	Secondary address or Command ($FF for no value)
Stack usage		2
Address		$FFBA, 65466
Returns	.A	preserved
	.X	preserved
	.Y	preserved

Preparation		OPEN
Send	.A	File number
	.X	ignored
	.Y	ignored
Stack usage		2
Address		$FFC3, 65475
Returns	.A	undefined
	.X	undefined
	.Y	undefined

Preparation		[OPEN]
Send	.A	ignored
	.X	ignored
	.Y	ignored
Stack usage		11
Address		$FFE7, 65511
Returns	.A	undefined
	.X	undefined
	.Y	preserved

Preparation		OPEN
Send	.A	ignored
	.X	File number
	.Y	ignored
Stack usage		0
Address		$FFC6, 65478
Returns	.A	undefined
	.X	undefined
	.Y	reserved

Preparation		OPEN
Send	.A	ignored
	.X	File number
	.Y	ignored
Stack usage		4+
Address		$FFC9, 65481
Returns	.A	undefined
	.X	undefined
	.Y	preserved

Preparation		[OPEN, CHKIN]
Send	.A	ignored
	.X	ignored
	.Y	ignored
Stack usage		7+
Address		$FFCF, 65487
Returns	.A	Retrieved byte
	.X	undefined
	.Y	preserved

Preparation		[OPEN, CHKOUT]
Send	.A	Byte to send
	.X	ignored
	.Y	ignored
Stack usage		8+
Address		$FFD2, 65490
Returns	.A	undefined
	.X	preserved
	.Y	preserved

Preparation		none
Send	.A	ignored
	.X	ignored
	.Y	ignored
Stack usage		2
Address		$FFB7, 65463
Returns	.A	Status code
	.X	preserved
	.Y	preserved

A sequential file is simply a list of bytes. When a SEQ file is opened for reading, the bytes from beginning to end will be consecutively loaded into the computer with each GET# or INPUT# command. When it is opened for writing, the PRINT# command will tack its output bytes after each other sequentially in the file.

These files work exactly the same as sequential files, but the operating system looks at PRG files a little differently. The first two bytes in the file give the address to load the program to, and the remaining bytes are the program data to be loaded at that address. If the LOAD command is used with the ,1 option, this address is used to locate the loading point in memory. If it is omitted, the computer will load the file at the start of BASIC memory, usually $0801 (2049). The advantage of using PRG files over plain SEQ is that you can store the data as well as the address to be loaded to into the file, and ask the operating system to take care of the loading and storing into right place in memory.

You can treat SEQ files as PRG files by adding ,S to the end of the filename. For example, SAVE"PRG1,S",8 will save a SEQ file which is laid out like a PRG file: with the address at the beginning of the program. Likewise, LOAD"PRG1,S",8,1 will load the saved data back into its place in memory. Take care not to load SEQ files that do not have an address header, or the data will load in an unexpected location, probably crashing your computer.